1. Field of the Invention
This invention relates to a novel recording liquid and is particularly directed to a novel recording liquid suitable for use in a recording system which comprises ejecting recording liquid droplets through fine spouts (discharging orifices) from a recording head to accomplish recording.
2. Description of the Prior Art
For recording on media such as paper and the like with writing tools (fountain pen, felt pen, etc.), there have hitherto been used inks, which are solutions of various dyes in water or in organic solvent.
It is also known that recording liquids of similar compositions are used in the above so-called ink-jet recording systems, in which the ejection of recording liquids is effected by vibration of piezo oscillators, electrostatic attraction due to a high voltage applied, or some other action. However, the recording liquids for the ink-jet recording system is required to satisfy more regorous performance characteristics in comparison with the recording liquids for writing tools such as fountain pen and felt pen.
There are various types of ink-jet recording systems which are different in the methods of generating recording liquid droplets and of controlling the flying directions of the droplets.
An example thereof is illustrated referring to FIG. 1. The device of FIG. 1 is a recording unit which generates recording liquid droplets in response to signals applied to a piezo oscillator attached to a recording head. In FIG. 1, 1 is the recording head provided with a piezo oscillator 2a, vibrating plate 2b, inlet port 3 for the recording liquid, liquid-holding chamber 4, and discharging orifice 5. The recording liquid 7 is fed into the liquid-holding chamber 4 from a reservoir 6 through a feeding pipe 8. An intermediate treating means 9 such as a pump or filter is provided, if necessary, in the middle of the feeding pipe 8. Recording signals converted into pulsed signals by use of a signal-treating means 10 (e.g. a pulse-generating means) are applied to the piezo oscillator 2a to vary the pressure of the recording liquid in the liquid-holding chamber 4 according to the applied signals. In consequence, the recording liquid 7 is discharged in the form of droplets 11 through the orifice 5 to make a record on the surface of a recording medium 12.
Besides the above, various types of devices are known; for example, a modification of the device of FIG. 1 is known which has, as shown in FIG. 2, a liquid-holding chamber 4 in a nozzle form and a cylindrical piezo oscillator 2a around the chamber. The mechanism of generating droplets in this device is fundamentally the same as in the device of FIG. 1. According to another known device, electrically charged droplets of recording liquid are continuously produced and parts of the droplets are used for recording. In another known device, thermal energy corresponding to recording signals is applied to the recording liquid in the recording head to produce droplets of the recording liquid.
An example of the device utilizing thermal energy is illustrated referring to FIGS. 3A, 3B and 4. FIG. 3A is a cross-section view of a recording head 13 taken in the direction of ink flow and FIG. 3B is the cross-sectional view taken on line A-B of FIG. 3A.
The recording head 13 is made by bonding a glass, ceramic or plastic plate having an ink-passing channel 14 with a heating head 15 for the thermosensitive recording (it is shown in the form of thin films in the figures but is not limited to such a form) which serves to exert thermal energy to the ink. The heating head comprises a protecting film 16 made of, e.g. silicon oxide; aluminum electrodes 17-1 and 17-2; a heating resistor layer 18 made of, e.g. nichrome; a heat accumulating layer 19; and a substrate 20 made of, e.g. alumina having a good heat-releasing property.
The ink 21 is filled in the channel 14 up to its discharging orifice 22 and forms a meniscus there by the action of pressure P.
On applying an electric signal to the electrodes 17-1 and 17-2, the region represented by n of the heating head 15 rapidly generates heat, bubbles are formed in the ink 21 contacting with the region n, the meniscus of the ink is projected by the action of the resulting pressure, and an ink droplet 24 is discharged through the orifice 22 and flys toward a recording medium 25. FIG. 4 shows an external appearance of a multi-head, which is an array of such heads as shown in FIG. 1. The multi-head is made by bonding a glass plate 27 having a number of channel 26 with a heating heat 28 similar to the one illustrated in FIG. 3A.
The recording liquid used for ink-jet recording is basically composed of coloring matter (a dye or pigments) and a liquid medium (water, various organic solvents and mixtures thereof can be employed) for dissolving or dispersing it, and if necessary, contains some additives. Recording liquids of this type have been disclosed in, for example, Japanese Patent. Publication Nos. 8361/1975, 40484/1976, 13126/1977 and 13127/1977 and Japanese Patent Laid-Open No. 95008/1975.
For the ink-jet recording liquid, more strict performance characteristics are requested than for the general writing ink. Such requested performance characteristics are as follows:
(1) Physical properties of recording liquid such as viscosity, surface tension and electric conductivity are to meet discharge conditions (e.g. piezo element-driving voltage and frequency; size, shape and material of orifice).
(2) It is stable during a long-term storage without causing orifice clogging.
(3) It is quickly fixed onto recording media such as paper, film and the like, the outlines of the resulting ink dots are smooth, and blotting of the dotted ink is minimized.
(4) The color of the resulting image is clear and dense.
(5) The resulting image is excellent in wet fastness and light fastness.
(6) It does not attack any of materials (its container, connecting tubes, sealants, etc.) in contact therewith.
(7) It has no unpleasant smell, toxicity, inflammability, or the like.
It is very difficult for the recording liquid to secure the above characteristics at the same time. The above-cited recording liquids of the prior art are unsatisfactory in this point.
Characteristics of the recording liquid are much dependent upon properties of the coloring matter since the recording liquid is basically composed of coloring matter and its solvent or dispersing medium as stated above. Accordingly, it is very important in the art to choose coloring matter so as to provide the recording liquid with the above requested characteristics.